Conventional electricity power mains comprises three live conductors at different phases together with a neutral conductor and a ground conductor, with the neutral conductor being connected to ground at the transformer for each main distribution sector.
Thus, a current outlet on the premises of any user for powering single-phase equipment comprises two power terminals one of which is connected to one of the live conductors and the other of which is connected to the neutral conductor, together with a third or ground terminal which is connected to a local ground and which is intended for connection to the chassis of the equipment plugged into said outlet.
In order to avoid any risk of electrocution when a person who is poorly insulated from ground touches said live conductor, safety devices have been proposed which comprise a trip-switch mounted at least on said live conductor and suitable for interrupting the supply of electricity at least to the corresponding terminal, together with a circuit for controlling the trip-switch.
The purpose of the trip-switch control circuit is to detect leakage currents which exceed a relatively low threshold (less than 6 mA at 200 volts AC) between the live conductor and the third or local ground terminal. To this end, the control circuit is sensitive to the potential difference which exists between the local ground and the ground at the main distribution transformer when said leakage current flows, by virtue of the non-zero resistance between said two points.
Various control circuits have thus been proposed which make use, in particular, of semi-conductor devices which constitute controlled switches, e.g. thyristors.
Above-mentioned French patent application No. 81 03192 also proposes a trip-switch control circuit constituted by a rectifier bridge whose inputs are connected to a general ground zero potential point at the main distribution transformer and to said third terminal or local ground terminal, and the positive and negative output terminals of the rectifier bridge feed a relay winding whose contact is connected in series with the winding of the trip-switch.
From the safety point of view, this arrangement is generally satisfactory.
However, heretofore it was not possible to integrate such a safety circuit including a trip-switch conveniently in an electricity outlet.
More precisely, it has heretofore not been possible to design a trip-switch which is simultaneously reliable, cheap, and small enough to be integrated in a housing for an electrical outlet of standard size.
The present invention seeks to improve this situation.